1. Field of the Invention
The present invention relates to disk drives such as magnetic disk drives and optical disk drives, and particularly to a disk drive capable of high-speed high-precision positioning operation by cooperation between a high-response, small-stroke precise-movement actuator and a low-response, large-stroke rough-movement actuator.
2. Description of the Related Art
In order for a disk drive, for example, magnetic disk drive to access high-density recorded information with high speed, it is required that the magnetic head driven by the actuators be fast moved to a desired track (seek control) and forced to precisely follow the center of the desired track (following control). For this requirement, it is necessary to reduce the weight of the actuators and widen the frequency band of the positioning control system. The reduction of weight, however, will lower the rigidity. Thus, the upper mechanical resonance frequency of the actuators has a constant limit, and the frequency band of the positioning control system is restricted thereby. The current magnetic disk drive traces tracks about 3 xcexcm wide and positions the heads with an accuracy of about 0.3 xcexcm. In future, the magnetic disk drive will be required to trace tracks of less than 1 xcexcm in width and position the head with an accuracy of less than 0.1 xcexcm. In order to achieve this positioning precision, it is necessary to widen the frequency band of the control system from the present value of about 500 Hz to 2 kHz or higher.
There is a known technique in which the magnetic head can be positioned with high speed and with high precision by a combination of a rough-movement actuator formed of a voice coil motor and precise-movement actuators formed of piezo-electric elements or the like. For example, a gazette of JP-A-4-368676 discloses the technique in which the control system for the rough-movement actuator and the control system for the precise-movement actuators are cooperated to widen the frequency band of the control system.
The prior art solved a problem with the positioning control technique by use of precise-movement and rough-movement actuators for a single particular head specified by the host controller. However, many problems remain unsolved with the positioning control technique in which two or more heads using precise-movement and rough-movement actuators are simultaneously controlled with high speed and with high precision.
If data on the same cylinder can be read at a time by two or more heads, it will be possible to transfer a large amount of data to the host controller. To achieve fast data transfer, it is important to fundamentally increase the bit density and fast rotate the disk, but the increase of bit density is limited by the magnetic interference problem and a problem with the circuits for data transfer. Thus, if a plurality of data can be written and read at a time, data can be fast transferred without increasing the bit density.
In addition, if positional information previously recorded on disks can also be read at a time by two or more heads, the heads can be successively switched on the same cylinder. To achieve continuous transfer of data, it is important to fundamentally make the head switching transition time zero. However, the heads are shifted a few xcexcm or below due to the deformation caused by the heat from the carriage that support many heads. Thus, the head switching settling time cannot be made zero. If the positioning information can be read at a time by two or more heads, it is possible that while data is being read or written by a certain head, a preselected head is positioned on a predetermined cylinder, thus the head switching transition time being made zero. Therefore, it is important to establish the control technique for simultaneously positioning two or more heads with high speed and with high precision, and this problem must be solved.
Accordingly, it is an object of the invention to provide a disk drive and positioning control system that are able to achieve the fast and precise positioning operation by two or more high-response, small-stroke precise-movement actuators and a low-response, large-stroke rough-movement actuator operated in cooperation with each other.
In order to achieve the above object, the present invention proposes a disk drive including a rough-movement actuator having a stroke enough to cover all disk, first and second precise-movement actuators capable of being moved by the rough-movement actuator and having a small stroke, and means for controlling the first precise-movement actuator to position a first head at a first track on a first disk surface and at the same time the second precise-movement actuator to position a second head at a second track on a second disk.
In addition, according to the invention, there is provided a disk drive including a rough-movement actuator having a stroke enough to cover all disk, first and second precise-movement actuators capable of being moved by the rough-movement actuator and having a small stroke, and means for controlling the first precise-movement actuator to position a first head at a first track on a first disk surface, at the same time the second precise-movement actuator to position a second head at a second track on a second disk and the rough-movement actuator to follow the positioning operation and to be positioned at the center position between the located first and second heads.
Also, according to the invention , there is provided a disk drive including a rough-movement actuator having a stroke enough to cover all disk, first and second precise-movement actuators capable of being moved by the rough-movement actuator and having small strokes, a first head to be driven by the first precise-movement actuator, a second head to be driven by the second precise-movement actuator, and means for supplying the sum of the amount of displacement of the first precise-movement actuator and the amount of displacement of the second precise-movement actuator, a first error signal produced after comparing a position signal from the first head with a first target value, a second error signal produced after comparing a position signal from the second head with the first target, and a signal resulting from adding and averaging the sum of the position signals, the first error signal and the second error signal to a feed-back compensator of said rough-movement actuator.
Moreover, according to the invention, there is provided a disk drive including a rough-movement actuator having a stroke enough to cover all disk, first and second precise-movement actuators capable of being moved by the rough-movement actuator and having small strokes, a first head to be driven by the first precise-movement actuator, a second head to be driven by the second precise-movement actuator, and means for controlling the first head opposing the surface of a first disk to previously record positional information on the surface of the first disk at constant intervals and the second head opposing the surface of a second disk to previously record positional information on the surface of the second disk in such a manner that the positional information recorded on the second disk is shifted out of phase from that recorded on the surface of the first disk.
Furthermore, according to the invention, there is provided a disk drive including a rough-movement actuator having a stroke enough to cover all disk, first and second precise-movement actuators capable of being moved by the rough-movement actuator and having small strokes, a first head to be driven by the first precise-movement actuator, a second head to be driven by the second precise-movement actuator, and means for controlling the second head to be moved to a target track on the surface of a second disk which the second head faces while the first head is being controlled to follow a track on the surface of a first disk which the first head faces, and after the movement, for controlling the second head to be switched to from the first head so that data can be written or read on or from the second disk.
The above countermeasures can be applied to other disk drives having three or more heads and three or more precise-movement actuators.